The present invention is a membrane coated substrate. More particularly, the present invention is a membrane coated paper suited for use with a color ink jet printer.
In recent years there have been advances in printing technology that permit the production of high resolution color images through ink jet printing. These advances make it possible for a user to record a color image in a digital format, transfer the image to a computer, manipulate the image, and then print the image on an ink jet printer. Current digital imaging systems are now capable of producing near photographic quality color images.
Improvements in the quality of color images produced by ink jet printers have resulted from developments in the components of the ink jet printer, such as printing heads, as well as advances in the ink compositions used in the ink jet printers. As a result of these developments in color ink jet printing, a new factor limiting the resolution and appearance of color images produced by ink printers has emerged. This limiting factor is the media on which the image is printed.
Using uncoated paper for ink jet printing produces less than optimum resolution because fibers in the paper cause the ink to "run." Additionally, uncoated papers are typically not glossy and therefore do not give photographic quality output.
In attempt to improve the performance of paper used with ink jet printers, a plastic layer has been extruded on the surface of the paper. The extruded plastic layer can give enhanced gloss, smoothness, and general appearance and is typically coated with materials that help to prevent the ink from running.
A drawback of extruded plastic paper coatings is that they typically have little or no porosity or liquid absorptivity. Consequently, the surface of these papers remain wet to the touch for an extended period of time as the ink drying mechanism is mainly due to evaporation of the ink solvent, which is frequently water. It may take ten minutes or more for the images to completely dry, depending on the temperature and humidity. Because of this lengthy drying time, each printed sheet must be removed from the printer tray and set out to dry to prevent smudging or carryover of the printed image onto the back side of the next printed sheet. Also, this extended period of wet ink on the paper surface makes it more likely that the ink will run, lowering image quality.
Another attempt to improve the performance of paper used with ink jet printers involves placing a porous coating on a support medium. The porous coating enhances ink absorption and thereby reduces the ink dry times. For example, Hershey et al., U.S. Pat. No. 4,154,899, describes a coating having a high solids content that is primarily formed from one or more pigments, one or more adhesives, and a small amount of other additives, such as anti-foaming agents.
It has also been disclosed to use inorganic particles to impart porosity to the porous coating. For example, Miyamoto et al., U.S. Pat. No. 4,460,637, describes forming the coating with an upper layer and a lower layer. The upper layer has a pore radius distribution of between 0.2 and 10 micrometers. The lower layer has a pore radius distribution of less than 0.05 micrometers. The Miyamoto et al. coating is prepared by mixing granular pigments with a polymeric binder and then casting the coating on a substrate.
Otouma et al., U.S. Pat. No. 4,780,356, discloses a porous membrane coated ink absorbent paper created by coating a mineral/binder combination on paper, in which the mineral particles themselves can be porous. Otouma et al. indicates that the porosity arises from the minerals particles themselves as well as from pore channels in some spaces between the mineral particles.
Misuda et al., U.S. Pat. No. 5,104,730, describes forming a silica layer on top of a porous coating, which is fabricated from porous particles in a polymeric binder. Misuda et al., U.S. Pat. No. 5,264,275, discusses forming a two-layer coating in which a lower layer has a smaller pore size and an upper layer has a larger pore size.
Suzuhi et al., U.S. Pat. No. 5,463,178, discloses forming a porous coating from pseudo-boehmite and then applying a scratch resistant uppermost layer of silica gel. Misuda et al., U.S. Pat. No. 5,472,773, describes producing a high gloss porous coated paper by first casting a porous layer from a pseudo-boehmite containing liquid on a smooth plastic sheet. A paper backing is then applied to the porous layer. Finally, the plastic sheet is separated from the porous layer to reveal the coated paper.
Others have found that ink absorbent coatings for ink jet recording media can be prepared using coatings that are free from inorganic filler particles. However, particles are still required in those methods to produce a porous coating. For example, Walchli, U.S. Pat. No. 5,374,475, describes preparing a polymeric solution and then adding a non-solvent to create microscopically small polymer particles. This polymer solution containing the microscopically small polymer particles is cast on a support media and then heat-treated to evaporate the solvents.
Yet another mechanism for improving the performance of media used with ink jet printers involves applying a low porosity ink absorbent coating to the media, such as is described in Senoo et al., U.S. Pat. No. 4,877,688. In Senoo et al., the coating is fabricated by layering a polymeric emulsion on a plastic substrate. Hasegawa et al., U.S. Pat. No. 4,954,395, discloses sandwiching an ink receiving layer between a non-porous polyester film and a porous coating, where the porous coating is formed from a coating mixture containing polymer micro-particles.